In high speed vehicular operation (especially when significant vehicular weights are involved) a vehicle suspension system capable of load sharing between longitudinally separated wheels is necessary to prevent the subjection of terrain induced impact loads on the vehicle chassis, reduce the load carrying capability of individual support wheels, and maintain a stable chassis orientation regardless of the terrain. The following U.S. patents illustrate typical longitudinal load sharing capability for high speed vehicles: U.S. Pat. Nos. 3,254,738; 3,740,070; 3,879,052; 4,047,736; 4,230,341; and 4,420,167.
Low speed, work vehicles in contradistinction to high speed vehicles, additionally require lateral side to side load sharing for maintaining maximum tractive engagement with the terrain. Such work vehicles often have an implement attached either to the front or rear end of the chassis whose purpose is, depending on the application, to exert either an upward or downward penetrating force on the earth. In such instances maximum force on the implement can be exerted by vertically pivoting the entire vehicle's chassis about the frontmost or rearmost (depending on the mounting location of the implement and the desired direction of force application) ground engaging member which usually constitutes a wheel. Such vehicle chassis pivoting can only be accomplished if longitudinal load sharing is not permitted between ground engaging members adjacent the chassis end in question and the remaining ground engaging members. None of the above patents has such implement application force maximizing capabilities.
Only recently has the inherent tractive advantage of track laying vehicles been combined with the high speed travel capability of wheel equipped vehicles to provide a work vehicle supported on and driven by elastomeric belts. In general, such work vehicle includes on each lateral side of its frame, wheels arranged in supporting relation to its frame and entrained within such belt with at least one of such wheels being frictionally engaged with the belt. With the advent of such work vehicle, both high speed mobility and low speed draft work may be optimally accomplished with one vehicle. However, use of a high speed suspension system on a belted vehicle also necessitates maintaining engagement between the belt and entrained wheels for all configurations assumable by those wheels in order to guide the belt and prevent it from being thrown from its entraining position around same. None of the above described patents has such belt to wheel engagement assurance provisions.
U.S. Pat. No. 3,254,738 ('738) provides the desired side to side load sharing and certain aspects of longitudinal load sharing between wheels/idlers using hydraulic circuits exclusively without any mechanical connection of the wheels. The '738 patent lacks provisions for maximizing the vehicle's capability of exerting penetration force on attached implements by virtue of the vehicle's longitudinal load sharing between wheels; and provides the side to side load sharing in a very complex hydraulic manner.
To take full advantage of a belted vehicle's high speed travel capabilities as well as its tractive advantages in low speed work applications, its suspension system must be able to provide the dynamic characteristics best suited for the operational mode selected (be it high speed or low speed) and do so with a minimum of complexity.